New laws to prevent radicalisation on campus have been branded “obnoxious” and an attack on free speech by one of the UK’s most senior lawyers.

Sir Ken Macdonald, former director of public prosecutions, said the Counter Terrorism and Security Act – which came into force this month – would have a chilling effect on intellectual debate and inquiry at universities.

Speaking at an event organised by Index on Censorship at Birkbeck, University of London on 1 July, Sir Ken said the new statutory duty to prevent extremist radicalisation on campus was, in effect, a way to “limit speech which is not otherwise criminal”.

Under the new rules, university staff must have “sufficient training have to be able to recognise vulnerability to being drawn into terrorism, and be aware of what action to take to take”.

Universities must also have “sufficient notice” about external speakers – generally at least 14 days – to ensure checks are made and the event cancelled if necessary.

Academics have complained they will be required to report their students to senior management or security authorities if they articulate highly politicised views. It may amount to racial profiling given the focus on Muslim extremism, some have said.

“Universities are environments that should tolerate all speech that is not criminal speech,” said Sir Ken, a Liberal Democrat life peer and warden of Wadham College, Oxford.

“No one I know is saying you should be able to go to university and call for the killing of British soldiers,” he said, pointing out that this would constitute an offence under incitement to cause harm.

However, certain subjects that did not accord with Western liberal values should still be open for discussion, he said.

“It is not illegal to say you are against democracy – Plato was against democracy – but the government wants to stop people saying that,” he said.

He pointed out that universities had a duty to protect free speech under the 1986 Education Act, which was introduced to ensure Tory ministers – notably former education secretary Keith Joseph – were allowed to speak at universities after having been “no platformed” by some student unions.

“Universities and students are being complicit in trying to limit free speech which is not otherwise criminal and would not lead to an act of violence,” he said.

Asked if a policy that required all external speakers to be recorded might assuage concerns about their talks – thereby lifting the need to vet speakers – Sir Ken said this was “a completely inappropriate response to a perceived threat and I do not think we should dignify it”.

Sir Ken also hit out at the University of Southampton, claiming the reasons given for the cancellation of its controversial conference on Israel – that it could not guarantee the safety of attendees in face of expected protests – were spurious.

“I do not believe anyone at Southampton was under any security threat,” he said.

“It was the easiest way out to say there was a security threat”, adding that he was “very, very suspicious [when] organisers [say] they cannot guarantee the safety of their guests”. Cancelling a conference on such grounds amounted to a “heckler’s veto”, he added.

However, Nicola Dandridge, chief executive of Universities UK, said Southampton had resisted calls to cancel the event for many weeks and safety concerns must be heeded.

Universities that could not hold such events should “ensure the issues are debated” in another manner, she added.

Other speakers at the event included free speech campaigner Greg Lukianoff, president and chief executive for the Foundation for Individual Rights in Education, and Julie Bindel, a journalist and feminist campaigner against sexual violence, who has been “no platformed” in a number of countries, including in the UK by student union branches.